Amphibians and many reptiles have three-chambered hearts, allowing some mixing of oxygenated and deoxygenated blood, as their body temperature depends on the external environment.

Birds and mammals have a separated heart to prevent the mixing of oxygenated and deoxygenated blood, ensuring efficient oxygen supply for their high energy needs.

De-oxygenated blood from the body enters the right atrium, which contracts to transfer the blood to the right ventricle. The right ventricle then pumps this blood to the lungs for oxygenation.

The left atrium collects oxygen-rich blood from the lungs, and upon contraction, transfers it to the left ventricle. The left ventricle then pumps the oxygenated blood to the rest of the body.

The heart has different chambers to prevent the mixing of oxygen-rich and carbon dioxide-rich blood. This separation ensures efficient oxygenation and removal of carbon dioxide.

A pumping organ is needed to push blood around the body, and the network of tubes ensures the distribution of blood to all tissues, providing nutrients and oxygen.

Oxygen is carried by red blood corpuscles in the blood.

Plasma is the fluid medium in blood, transporting food, carbon dioxide, nitrogenous wastes, salts, and other substances in dissolved form.

Carbon dioxide, more soluble in water than oxygen, is mainly carried in its dissolved form in the blood.

Haemoglobin, a respiratory pigment in red blood cells, has a high affinity for oxygen, facilitating its transport from the lungs to oxygen-deficient tissues.